Iran's President Hassan Rouhani has hit out at the United States over its reinstatement of economic sanctions.
He described the measures, which came into effect overnight, as "psychological warfare" which aimed to "sow division among Iranians".
The sanctions take aim at various sectors, with further punitive action planned against Iran's oil trade.
The European Union has spoken out against the measures, vowing to protect firms doing "legitimate business".
It follows the US withdrawal from the Joint Comprehensive Plan of Action, also known as the Iran nuclear deal, earlier this year.
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The deal, negotiated during the presidency of Barack Obama, saw Iran limit its controversial nuclear activities in exchange for sanctions relief.
Mr Trump says the deal is "one-sided" and he believes renewed economic pressure will force Iran to agree to a new deal and end its "malign" activities.
What are the sanctions?
US President Donald Trump signed an executive order which brought sanctions back into place at 00:01 EDT (04:01 GMT) on Tuesday. They target:
- The purchase or acquisition of US banknotes by Iran's government
- Iran's trade in gold and other precious metals
- Graphite, aluminium, steel, coal, and software used in industrial processes
- Transactions related to the Iranian rial currency
- Activities relating to Iran's issuance of sovereign debt
- Iran's automotive sector
A second phase is planned to come back into effect on 5 November which will have implications for Iran's energy and shipping sectors, petroleum trading and transactions by foreign financial institutions with the Central Bank of Iran.
Why is the US implementing them?
The imposing of sanctions follows Mr Trump's withdrawal from the 2015 deal earlier this year.
Mr Trump had long spoken out against the agreement, labelling it "disastrous" and the "worst deal I've ever seen".
Only the US has withdrawn, with other signatories remaining committed to the original agreement. But Iran's currency has lost almost half of its value since, squeezing the economy.
Mr Trump says Iran faces a choice to "either change its threatening, destabilizing behaviour and reintegrate with the global economy, or continue down a path of economic isolation".
"I remain open to reaching a more comprehensive deal that addresses the full range of the regime's malign activities, including its ballistic missile program and its support for terrorism," Mr Trump said on Monday.
What has the reaction been?
Mr Rouhani rebuked Mr Trump's decision to reinstate sanctions, saying the US government had "turned their back on diplomacy" with the action.
"They want to launch psychological warfare against the Iranian nation." Mr Rouhani said. "Negotiations with sanctions doesn't make sense."
"We are always in favour of diplomacy and talks... but talks need honesty."
He also accused the Trump administration of using Iran as domestic political leverage ahead of November's midterm elections in the United States.
The foreign ministers of Germany, the UK and France released a statement on Monday that said the nuclear deal remained "crucial" to global security.
They also unveiled a "blocking statute" which is intended to protect European firms doing business with Iran despite the new US sanctions.
The US had previously rejected calls to offer exemptions, with Mr Trump vowing "severe consequences" against firms and individuals who continued to trade with Iran.
An anonymous senior official told US media that the administration was "not particularly concerned" by EU protection efforts.